1. Field of the Invention
The present invention relates to an optical disc apparatus and, in particular, to an optical disc apparatus in which the optical path for the output light from the light source consisting of a semiconductor laser or the like and the reflected light from the optical disc is formed by a polarization-preserving optical fiber.
2. Description of the Related Art
ROM (read only memory) type optical discs such as CDs (compact discs) and RAM (random access memory) type optical discs such as phase change discs and magneto-optical discs are widely used as media for storing information such as image information, sound information or programs for information apparatuses in the form of pit patterns, recording marks, etc. The density and capacity of such optical discs are gradually increasing, and, in optical disc apparatuses for these discs, the diameter of the light spot condensed through an objective lens is reduced by, for example, reducing the wavelength of the semiconductor laser or increasing the NA (numerical aperture) of the objective lens. For example, in the CDs commercially manufactured in relatively early times, the wavelength of the light source is set to be 780 nm, whereas in the DVDs (digital video discs or digital versatile discs) commercially manufactured in recent times, the wavelength of the light source is set to be 650 nm or 635 nm. Recently, a further increase in the density and capacity of the optical disc is desired and realized, and an optical disc apparatus which is compatible with both a ROM type and a RAM type optical disc is required.
It is an object of the present invention to provide an optical disc apparatus which is compatible with both a ROM type and a RAM type optical disc having high density and large capacity.
To achieve the above object, there is provided, according to Claim 1 of the present invention, an optical disc apparatus comprising:
disc control means including
an optical disc;
a spindle motor for rotating the optical disc at a predetermined speed;
an objective lens for forming a light spot on the optical disc; and
control drive means which forms a rotary linear motor in which the objective lens is secured to one end of an arm that rotates around a central shaft provided at the other end of the arm and which controls and drives the objective lens in the tracking direction of the optical disc;
a light source formed by a semiconductor laser or the like;
signal light transfer means in which the optical path for guiding output light from the light source to the objective lens is formed of a polarization-preserving optical fiber;
a wave plate provided in an optical path on either side of the polarization-preserving optical fiber; and
signal detecting means for receiving the reflected light from the optical disc and subjecting it to photoelectric conversion to detect, for example, a focusing error signal, a tracking error signal, a servo signal supplying information on the position on the optical disc where recording or reproduction is effected, and an RF signal.
According to Claim 2 of the present invention, there is provided an optical disc apparatus comprising:
disc control means including
a plurality of optical discs;
a spindle motor for rotating the plurality of optical discs integrally and at a predetermined speed;
a plurality of objective lenses for forming light spots on the individual optical discs; and
control drive means for controlling and driving a plurality of objective lenses integrally in the tracking direction of the optical disc;
a light source formed, for example, by a semiconductor laser;
signal light transfer means in which the optical paths for guiding output light from the light source to the individual objective lenses are formed of a plurality of polarization-preserving optical fibers;
a wave plate provided in the optical path on either side of the plurality of polarization-preserving optical fibers;
signal optical path switching means which includes decentered light emitting means which is arranged between the light source and the signal light transfer means and which selects one output light from the light source from among the plurality of polarization-preserving optical fibers, for example, outputs incident light incident in conformity with the rotation center axis from a position parallel to and decentered from the rotation center axis and in which the plurality of polarization-preserving optical fibers are arranged in a circumference in conformity with the optical axis of the output light from the decentered light emitting means; and
signal detecting means which receives the reflected light from the optical disc and subjects it to photoelectric conversion to detect, for example, a focusing error signal, a tracking error signal, a servo signal providing positional information on the position of the optical disc where recording or reproduction is effected, and an RF signal.
According to Claim 3 of the present invention, there is provided a disc apparatus comprising:
disc control means including
a plurality of optical discs;
a spindle motor for rotating the plurality of optical discs integrally and at a predetermined speed;
a plurality of objective lenses for forming light spots on the individual optical discs; and
control drive means which forms, for example, a rotary linear motor in which the objective lens is secured to one end of an arm that rotates around a central shaft provided at the other end of the arm and which controls and drives the objective lens independently in the tracking direction of the optical discs with respect to the individual optical discs, that is, control drive means in the same number as the optical discs and operating independently;
a light source formed, for example, by a semiconductor laser;
signal light transfer means in which the optical paths for guiding output light from the light source to the individual objective lenses are formed of a plurality of polarization-preserving optical fibers;
a wave plate provided in the optical path on either side of the plurality of polarization-preserving optical fibers;
signal optical path switching means which includes decentered light emitting means which is arranged between the light source and the signal light transfer means and which selects one output light from the light source from among the plurality of polarization-preserving optical fibers, for example, outputs incident light incident in conformity with the rotation center axis from a position parallel to and decentered from the rotation center axis and in which the plurality of polarization-preserving optical fibers are arranged in a circumference in conformity with the optical axis of the output light from the decentered light emitting means; and
signal detecting means which receives the reflected light from the optical disc and subjects it to photoelectric conversion to detect, for example, a focusing error signal, a tracking error signal, a servo signal providing positional information on the position of the optical disc where recording or reproduction is effected, and an RF signal.
It is desirable for the angle of the crystal axis of the wave plate in the optical disc apparatus as claimed in Claims 1, 2 and 3 to be inclined (45+90xc3x97N) degrees with respect to the refractive index distribution axis of the polarization-preserving optical fiber (the axis connecting the centers of stress imparting portions paired with the clad, that is, the portions where refractive index distribution exists, in the section cut from a direction perpendicular to the longitudinal direction of the polarization-preserving optical fiber).
According to Claim 8 of the present invention, there is provided an optical disc apparatus comprising:
disc control means including
an optical disc;
a spindle motor for rotating the optical disc at a predetermined speed;
an objective lens for forming a light spot on the optical disc; and
control drive means which forms a rotary linear motor in which the objective lens is secured to one end of an arm that rotates around a central shaft provided at the other end of the arm and which controls and drives the objective lens in the tracking direction of the optical disc;
a light source formed, for example, by a semiconductor laser;
signal light transfer means in which the optical path guiding the output light from the light source to the objective lens is formed by one polarization-preserving optical fiber formed by joining two polarization-preserving optical fibers in which the refractive index distribution axes are caused to intersect each other at right angles to cancel the phase difference generated in the polarization-preserving optical fibers; and
signal detecting means for receiving the reflected light from the optical disc and subjecting it to photoelectric conversion to detect, for example, a focusing error signal, a tracking error signal, a servo signal supplying information on the position on the optical disc where recording or reproduction is effected, and an RF signal.
According to Claim 9 of the present invention, there is provided an optical disc apparatus comprising:
disc control means including
a plurality of optical discs;
a spindle motor for rotating the plurality of discs integrally at a predetermined speed;
a plurality of objective lenses for forming light spots on the individual optical discs; and
control drive means for controlling and driving the plurality of objective lenses integrally in the tracking direction of the optical discs;
a light source formed, for example, by a semiconductor laser;
signal light transfer means in which the optical path guiding the output light from the light source to the individual objective lenses is formed by a plurality of polarization-preserving optical fibers formed by joining two polarization-preserving optical fibers in which the refractive index distribution axes are caused to intersect each other at right angles to cancel the phase difference generated in the polarization-preserving optical fibers;
signal optical path switching means which includes decentered light emitting means which is arranged between the light source and the signal light transfer means and which selects one output light from the light source from among the plurality of polarization-preserving optical fibers, for example, outputs incident light incident in conformity with the rotation center axis from a position parallel to and decentered from the rotation center axis and in which the plurality of polarization-preserving optical fibers are arranged in a circumference in conformity with the optical axis of the output light from the decentered light emitting means; and
signal detecting means for receiving the reflected light from the optical disc and subjecting it to photoelectric conversion to detect, for example, a focusing error signal, a tracking error signal, a servo signal supplying information on the position on the optical disc where recording or reproduction is effected, and an RF signal.
According to Claim 10 of the present invention, there is provided an optical disc apparatus comprising:
disc control means including
a plurality of optical discs;
a spindle motor for rotating the plurality of optical discs integrally at a predetermined speed;
a plurality of objective lenses for forming light spots on the individual optical discs; and
control drive means, that is, control drive means in the same number as the optical discs and operating independently, which controls and drives the objective lenses independently in the tracking direction of the optical discs relative to the individual optical discs and which forms a rotary linear motor in which, for example, the objective lens is secured to one end of an arm that rotates around a central shaft provided at the other end of the arm;
a light source formed, for example, by a semiconductor laser;
signal light transfer means in which the optical path guiding the output light from the light source to the individual objective lenses is formed by a plurality of polarization-preserving optical fibers formed by joining two polarization-preserving optical fibers in which the refractive index distribution axes are caused to intersect each other at right angles to cancel the phase difference generated in the polarization-preserving optical fibers;
signal optical path switching means which includes decentered light emitting means which is arranged between the light source and the signal light transfer means and which selects one output light from the light source from among the plurality of polarization-preserving optical fibers, for example, outputs incident light incident in conformity with the rotation center axis from a position parallel to and decentered from the rotation center axis and in which the plurality of polarization-preserving optical fibers are arranged in a circumference in conformity with the optical axis of the output light from the decentered light emitting means; and
signal detecting means for receiving the reflected light from the optical disc and subjecting it to photoelectric conversion to detect, for example, a focusing error signal, a tracking error signal, a servo signal supplying information on the position on the optical disc where recording or reproduction is effected, and an RF signal.
In the optical disc apparatus according to Claims 1 and 8 of the present invention, the optical disc attached to the spindle motor may be ROM type or RAM type. Further, in the optical disc apparatus according to Claims 2, 3, 9 and 10 of the present invention, the plurality of optical discs attached to the spindle motor are all ROM type optical discs, all RAM type optical discs, or ROM type optical discs and RAM type optical discs mixed together in an arbitrary proportion.
The operation of the above-described means is as follows.
In the optical discs according to Claims 1, 2 and 3 of the present invention, in which a wave plate is arranged in the optical path on either side of the polarization-preserving preserving optical fiber, the signal light which involves a change in quantity of light as in the case of a pit pattern disc and a phase change disc is transmitted without being influenced, and, in the case of a magneto-optical disc, it is possible to correct the phase difference of the electric field oscillation component perpendicular to the magneto-optical signal light. Further, in the optical discs according to Claims 8, 9 and 10, in which the optical path is formed by a polarization-preserving optical fiber formed by joining two polarization-preserving optical fibers the refractive index distribution axes of which are perpendicular to each other, the signal light reflected by the optical disc and returned is transmitted without being influence as in the case of a pit pattern disc and a phase change disc, and, in the case of a magneto-optical disc, the phase difference generated in the polarization-preserving optical fiber can be canceled. Further, in the optical disc apparatus according to Claims 2, 3, 9 and 10, in which a plurality of optical discs are attached to the spindle motor, there is no need to prepare a dedicated optical source, photo detector, etc. for each optical disc due to the signal optical path switching means, whereby it is possible to construct a simple optical system.